diff --git a/.github/workflows/publish-releases.yaml b/.github/workflows/publish-releases.yaml
index 58a8378..cde2af2 100644
--- a/.github/workflows/publish-releases.yaml
+++ b/.github/workflows/publish-releases.yaml
@@ -41,9 +41,18 @@ jobs:
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
-          ref: ${{ github.event.release.tag_name }}
+          ref: main
           fetch-depth: 0
 
+      - name: Validate release tag
+        id: release
+        env:
+          TAG_NAME: ${{ github.event.release.tag_name }}
+        run: ./scripts/validate-release-tag.sh
+
+      - name: Check out validated release tag
+        run: git checkout --detach "$(git rev-parse 'refs/tags/${{ steps.release.outputs.tag }}^{}')"
+
       - name: Install uv
         uses: astral-sh/setup-uv@caf0cab7a618c569241d31dcd442f54681755d39 # v3.4.1
 
@@ -53,7 +62,12 @@ jobs:
           python-version: "3.13"
 
       - name: Build package
-        run: uvx --with uv-dynamic-versioning hatchling build -d ./dist/
+        env:
+          RELEASE_VERSION: ${{ steps.release.outputs.version }}
+        run: |
+          package_version=$(uvx --with uv-dynamic-versioning hatchling version)
+          test "$package_version" = "$RELEASE_VERSION"
+          uvx --with uv-dynamic-versioning hatchling build -d ./dist/
 
       - name: Publish to PyPI
         uses: pypa/gh-action-pypi-publish@dc37677b2e1c63e2034f94d8a5b11f265b73ba33 # release/v1
diff --git a/scripts/validate-release-tag.sh b/scripts/validate-release-tag.sh
new file mode 100755
index 0000000..8a81a88
--- /dev/null
+++ b/scripts/validate-release-tag.sh
@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+: "${TAG_NAME:?TAG_NAME must be set}"
+
+if [[ ! "$TAG_NAME" =~ ^v[0-9]+\.[0-9]+\.[0-9]+$ ]]; then
+  printf 'Release tag %q is not a canonical lowercase tag in vMAJOR.MINOR.PATCH form.\n' "$TAG_NAME" >&2
+  exit 1
+fi
+
+git fetch --no-tags origin main
+
+tag_commit=$(git rev-parse "refs/tags/$TAG_NAME^{}")
+main_commit=$(git rev-parse FETCH_HEAD)
+
+if [[ "$tag_commit" != "$main_commit" ]]; then
+  printf 'Release tag %s (%s) does not point to origin/main (%s).\n' "$TAG_NAME" "$tag_commit" "$main_commit" >&2
+  exit 1
+fi
+
+{
+  printf 'tag=%s\n' "$TAG_NAME"
+  printf 'version=%s\n' "${TAG_NAME#v}"
+} >> "$GITHUB_OUTPUT"
diff --git a/tests/test_release_guard.py b/tests/test_release_guard.py
new file mode 100644
index 0000000..2bc5df5
--- /dev/null
+++ b/tests/test_release_guard.py
@@ -0,0 +1,85 @@
+import os
+import subprocess
+from pathlib import Path
+
+import pytest
+
+
+REPOSITORY_ROOT = Path(__file__).parents[1]
+GUARD = REPOSITORY_ROOT / "scripts" / "validate-release-tag.sh"
+
+
+def run(command: list[str], cwd: Path) -> subprocess.CompletedProcess[str]:
+    return subprocess.run(command, cwd=cwd, check=True, capture_output=True, text=True)
+
+
+@pytest.fixture
+def release_repository(tmp_path: Path) -> Path:
+    remote = tmp_path / "remote.git"
+    repository = tmp_path / "repository"
+
+    run(["git", "init", "--bare", str(remote)], tmp_path)
+    run(["git", "clone", str(remote), str(repository)], tmp_path)
+    run(["git", "config", "user.email", "test@example.com"], repository)
+    run(["git", "config", "user.name", "Test User"], repository)
+    (repository / "README").write_text("initial\n")
+    run(["git", "add", "README"], repository)
+    run(["git", "commit", "-m", "initial"], repository)
+    run(["git", "branch", "-M", "main"], repository)
+    run(["git", "push", "-u", "origin", "main"], repository)
+    return repository
+
+
+def guard(tag_name: str, repository: Path) -> subprocess.CompletedProcess[str]:
+    output = repository / "github-output"
+    return subprocess.run(
+        [str(GUARD)],
+        cwd=repository,
+        env={**os.environ, "TAG_NAME": tag_name, "GITHUB_OUTPUT": str(output)},
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+
+
+def test_accepts_canonical_tag_at_origin_main(release_repository: Path) -> None:
+    run(["git", "tag", "v0.0.67"], release_repository)
+    run(["git", "push", "origin", "v0.0.67"], release_repository)
+
+    result = guard("v0.0.67", release_repository)
+
+    assert result.returncode == 0
+
+
+def test_rejects_noncanonical_uppercase_tag(release_repository: Path) -> None:
+    run(["git", "tag", "V0.0.67"], release_repository)
+    run(["git", "push", "origin", "V0.0.67"], release_repository)
+
+    result = guard("V0.0.67", release_repository)
+
+    assert result.returncode != 0
+    assert "canonical lowercase tag" in result.stderr
+
+
+def test_rejects_tag_behind_updated_origin_main(
+    release_repository: Path, tmp_path: Path
+) -> None:
+    run(["git", "tag", "v0.0.67"], release_repository)
+    run(["git", "push", "origin", "v0.0.67"], release_repository)
+
+    updater = tmp_path / "updater"
+    run(
+        ["git", "clone", str(release_repository.parent / "remote.git"), str(updater)],
+        tmp_path,
+    )
+    run(["git", "config", "user.email", "test@example.com"], updater)
+    run(["git", "config", "user.name", "Test User"], updater)
+    run(["git", "checkout", "main"], updater)
+    (updater / "README").write_text("updated\n")
+    run(["git", "commit", "-am", "advance main"], updater)
+    run(["git", "push"], updater)
+
+    result = guard("v0.0.67", release_repository)
+
+    assert result.returncode != 0
+    assert "does not point to origin/main" in result.stderr